The present invention relates to an electronic circuit which may be used in conjunction with conventional storage batteries to replace nickel-cadmium (or other types of) battery packs of the type used to power numerous types of portable electronic devices. In particular, the present invention relates to an electronic circuit which can be used on "host" equipment, such as forklifts, which already have large storage batteries, to convert the "dirty" power available from those storage batteries on such "host" equipment so that it can be used to power portable electronic equipment carried thereon, where such portable electronic equipment requires a source of "clean" power.
There are many applications in which portable electronic devices are powered by rechargeable batteries, such as nickel-cadmium ("NiCad") batteries. In view of the fact that NiCad battery packs far outnumber other types of rechargeable battery packs, as used herein the term "NiCad" is intended to include all types of rechargeable battery packs. The portable electronic devices employed in many of these applications require a source of transient-free, stable power, referred to herein as "clean" power. While rechargeable NiCad batteries can be used to supply such clean power, NiCad batteries have a number of problems which are well known by those skilled in the art. In particular, they require periodic recharging in order to provide power. However, if they are recharged too often, i.e., before they have fully discharged, they experience a phenomenon referred to as "memory", with the result that they need to be recharged sooner than if they were allowed to fully discharge prior to being recharged. On the other hand, if they are allowed to fully discharge prior to being replaced or recharged, so as to minimize problems with memory, then there is a possibility that they will discharge in operation. Obviously, that is not an acceptable situation, so, in real applications, it is typically necessary to replace and recharge NiCad batteries prior to the time that they become filly discharged.
Interestingly, there are a number of applications which employ NiCad batteries for powering portable electronic devices, in which the portable electronic devices are mounted on or in vehicles or other systems which are either powered by electricity or which have on-board rechargeable storage batteries. By way of example, devices such as bar code scanners, terminals, printers (including thermal printers and dot matrix printers), RF terminals, 2-way radios, data-links, computers, calculators, and numerous other devices typically require "clean", microprocessor grade, regulated power sources, even though they are often mounted on "host" systems, such as forklifts, which are already equipped with large storage batteries which could provide adequate power, but for the fact that the power available from the batteries on such host systems is especially prone to transients which are unacceptable in the operation of the portable electronic devices.
One example of such a combination of a battery equipped "host" on which a NiCad-powered portable electronic device is mounted is a bar code scanner mounted, either permanently or semi-permanently, on a forklift or battery operated hand truck. The NiCad batteries in the scanner normally last from two to six hours (depending upon the amount of use) before they require recharging. The large storage batteries which power the host system, on the other hand, last far longer, or (in the case of some host systems) recharge in operation.
There are also other problems with NiCad batteries. In particular, even though they are expensive, their life span may be as short as 100 recharges, depending upon their application and their recharging program. Also, disposal of NiCad batteries has become a problem due to the fact that they contain materials which are considered to be toxic.
In view of the above problems with NiCad batteries, it would be desirable to be able to power portable electronic devices which are mounted on host vehicles which have sources of electricity, by those electric power sources on the host vehicles, thereby eliminating the NiCad battery packs, along with the problems and costs associated with replacing battery packs when they become discharged, disposing of battery packs when they have reached the end of their useful life, and the expense of replacement NiCad battery packs.